Evolution: more gaps in foraminifera (Evolution)

"The fossil record provides empirical patterns of morphological change through time and is central to the study of the tempo and mode of evolution. Here we apply likelihood-based time-series analyses to the near-continuous fossil record of Neogene planktonic foraminifera and reveal a morphological shift along the Truncorotalia lineage. Based on a geometric morphometric dataset of 1,459 specimens, spanning 5.9–4.5 Ma, we recover a shift in the mode of evolution from a disparate latest Miocene morphospace to a highly constrained early Pliocene morphospace. Our recovered dynamics are consistent with those stipulated by Simpson's quantum evolution and Eldredge-Gould's punctuated equilibria and supports previous suppositions that even within a single lineage, evolutionary dynamics require a multi-parameter model framework to describe. We show that foraminiferal lineages are not necessarily gradual and can experience significant and rapid transitions along their evolutionary trajectories and reaffirm the utility of multivariate datasets for their future research.

"Conclusion
We documented and assessed the evolutionary transition along Truncorotalia across the Miocene/Pliocene boundary using semilandmark morphometrics and time-series analyses. A potentially localized and rapid evolutionary shift between two end members of Truncorotalia, T. juanai and T. crassaformis, at 5.1–5.2 Ma reveals that the evolutionary dynamics were not gradual and rejects the notion of an intermediate form along the lineage (contraArnold, 1983, Cifelli and Scott, 1986). The transition between end members involved a major reduction in morphological diversity and a transition to a more constrained morphological stock. Furthermore, likelihood-based time-series analyses strengthen this hypothesis through rejection of simple gradual or random modes of evolution, in favor of shift models, which can be interpreted within the context of both Simpson's QE and Eldredge and Gould's PE. Through this study we hope to augment research into tempo and mode in planktonic foraminifera and highlight certain expectations of Simpson's theory, which are not explicit to PE. We envision that application of these methods by planktonic foraminiferal researchers will garnish further explicit tests of tempo and mode in this iconic fossil group."

Comment: Very complex article, but it shows that another species, like the whales, have huge gaps between phenotypes. Nothing looks gradual in evolution. Gaps always demand consideration of design.